1. Field
The present disclosure relates to a steer-by-wire type vehicle steering device.
2. Description of the Related Art
Recently, a steering device of a type called steer-by-wire has been developed. Japanese Unexamined Patent Application Publication (JP-A) No. 2003-252227 discloses a steer-by-wire (SBW) type vehicle steering device.
In the SBW type vehicle steering device according to JP-A No. 2003-252227, a clutch device is interposed between a column shaft that is rotated according to an operation of the steering wheel and a transmission shaft that is rotated according to an operation of a steering mechanism to engage or disengage the connection therebetween. The steering control unit determines whether or not a steering motor is in an overload state based on the drive state (motor current and motor temperature) of the steering motor that steers turning wheels. In the case where the steering motor is determined to be in an overload state, the steering control unit switches the state of the clutch device from a disengaged state to an engaged state, thereby mechanically transmitting an operation force to the steering mechanism to perform steering, the operation force being applied to the steering wheel.
With the SBW type vehicle steering device according to JP-A No. 2003-252227, an occurrence of an overload in the steering motor may be reliably restrained.
In the SBW type vehicle steering device according to JP-A No. 2003-252227, in the case where a value for motor current (correlation value of a motor temperature) continues to exceed a predetermined threshold value for a predetermined time, the steering motor is determined to be in an overload state based on the motor current (or the motor temperature) supplied to the steering motor, and the state of the clutch device is switched from a disengaged state to an engaged state.
However, with the above-described configuration, in the case where an event, in which the motor current value (the motor temperature correlation value) exceeds the predetermined threshold value, occurs continuously and each event has a time period slightly shorter than the predetermined time, it is erroneously determined that the steering motor is not in an overload state although the steering motor is actually in an overload state. Consequently, timing for switching the state of the clutch device from a disengaged state to an engaged state is delayed with respect to proper switching timing, and thus the overload state of the steering motor may be prolonged.
Particularly, when determination is made based on the value of a motor temperature as to whether or not the steering motor is in an overload state, a temperature sensor such as a thermistor needs to be separately provided. Therefore, the number of components and the cost are increased.
It is to be noted that reliable determination as to whether or not a motor is in an overload state is demanded of not only the steering motor but also the steering reaction force motor.